Bipolar scr

ABSTRACT

A high-voltage bipolar semiconductor controlled rectifier (SCR) includes an emitter region having a first polarity and overlying a base region having a second polarity different from the first polarity; a collector region having the first polarity and lying under the base region; an anode region having the second polarity; a first sinker region having the first polarity and contacting the collector region, wherein the anode region is between the first sinker region and the base region; and a second sinker region having the first polarity and contacting the collector region, the second sinker region lying between the anode region and the base region, wherein an extension of the anode region extends under a portion of the second sinker region.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Nonprovisional patentapplication Ser. No. 15/088,681, filed Apr. 1, 2016, the contents ofwhich is herein incorporated by reference in its entirety.

FIELD OF THE DISCLOSURE

Disclosed embodiments relate generally to the field of integratedcircuit designs. More particularly, and not by way of any limitation,disclosed embodiment are directed to methods for implementing abipolar-based semiconductor controlled rectifier for an electrostaticdischarge protection circuit.

BACKGROUND

Integrated circuits are quite susceptible to damage from electrostaticdischarge from common environmental sources and can be destroyed whensubjected to voltages higher than their intended voltage supply.Electrostatic discharge (ESD) protection circuits are used to dischargecurrent from ESD events harmlessly, with silicon controlled rectifiers(SCR) providing an effective solution in a small area. However, issuesremain in the design of SCRs for high-voltage pins. A solution islacking with regard to a low-leakage, low-capacitance bipolar based SCRfor high voltage pins. Non-SCR based solutions are inefficient, whileexisting SCR designs suffer from high leakage due to punch-throughissues.

SUMMARY

The present patent application discloses an SCR that contains a blockingjunction to prevent punch through. The blocking junction is constructedby modifying the collector sinker region and introducing anode junctionsunder the modified sinker to enable SCR action. The modified sinker canbe used to change the trigger/holding current of the SCR and theconstruction allows for independent modification of the trigger currentwhile maintaining the immunity to PNP injection from the substrate.

In one aspect, an embodiment of a high-voltage bipolar semiconductorcontrolled rectifier (SCR) is disclosed. The SCR includes an emitterregion having a first polarity and overlying a base region having asecond polarity different from the first polarity; a collector regionhaving the first polarity and lying under the base region; an anoderegion having the second polarity; a first sinker region having thefirst polarity and contacting the collector region, wherein the anoderegion is between the first sinker region and the base region; and asecond sinker region having the first polarity and contacting thecollector region, the second sinker region lying between the anoderegion and the base region, wherein an extension of the anode regionextends under a portion of the second sinker region.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present disclosure are illustrated by way of example,and not by way of limitation, in the figures of the accompanyingdrawings in which like references indicate similar elements. It shouldbe noted that different references to “an” or “one” embodiment in thisdisclosure are not necessarily to the same embodiment, and suchreferences may mean at least one. Further, when a particular feature,structure, or characteristic is described in connection with anembodiment, it is submitted that it is within the knowledge of oneskilled in the art to effect such feature, structure, or characteristicin connection with other embodiments whether or not explicitlydescribed.

The accompanying drawings are incorporated into and form a part of thespecification to illustrate one or more exemplary embodiments of thepresent disclosure. Various advantages and features of the disclosurewill be understood from the following Detailed Description taken inconnection with the appended claims and with reference to the attacheddrawing figures in which:

FIG. 1 depicts a cross-sectional view of an SCR according to anembodiment of the disclosure;

FIG. 2 depicts a current-voltage diagram of the SCR of FIG. 1;

FIG. 3 depicts a cross-sectional view of an SCR according to anembodiment of the disclosure;

FIG. 4 depicts a cross-sectional view of an SCR according to anembodiment of the disclosure;

FIG. 5 depicts a plan view of the SCR of FIG. 1 according to anembodiment of the disclosure;

FIG. 6 depicts a plan view of the SCR of FIG. 1 according to anembodiment of the disclosure;

FIG. 7 depicts a plan view of the SCR of FIG. 1 according to anembodiment of the disclosure;

FIG. 8 depicts a plan view of the SCR of FIG. 1 according to anembodiment of the disclosure; and

FIG. 9 depicts an example embodiment of a bipolar SCR as known in theart.

DETAILED DESCRIPTION OF THE DRAWINGS

Specific embodiments of the invention will now be described in detailwith reference to the accompanying figures. In the following detaileddescription of embodiments of the invention, numerous specific detailsare set forth in order to provide a more thorough understanding of theinvention. However, it will be apparent to one of ordinary skill in theart that the invention may be practiced without these specific details.In other instances, well-known features have not been described indetail to avoid unnecessarily complicating the description.

Referring now to the drawings and more particularly to FIG. 9, across-sectional view of a prior art SCR 900 is shown. SCR 900 is builton a bipolar transistor, i.e., the NPN transistor formed by n-typeregion N-Emitter 902, which is formed over p-type region P-Base 904 andan underlying n-type collector formed by Region 906, n-type buried layerextension (NBLX) 908 and n-type buried layer (NBL) 910. The collector iscontacted by n-type Sinker 918, which is formed by three differentimplantations, referred to herein as n-type source/drain (NSD), n-typedeep well (DEEPN) and NBLX. The cross-hatched areas represent ShallowTrench Isolation 920 or other dielectric layers. Since this example isan NPN transistor, a heavily doped p-type layer, here p-typesource/drain (PSD) 914, is inserted into the NPN transistor to create aPNPN structure that acts as an SCR. SCR 900 works well at voltages inthe range of 3-5 volts, but when higher voltages are used, multipleissues arise. One issue is punch-through; for example, whenever areverse bias is applied from P-Base 904 to Region 906, the field canpotentially go all the way to the anode, PSD 914, as shown by the arrowsin this figure. This situation shorts out one of the internal bipolartransistors, giving a very leaky SCR at a very low voltage, so that SCR900 can't hold high voltages at low current. Other issues can alsoarise, such as parasitic MOS transistors or charges on the shallowtrench isolation that can cause a short, but basically, at a very lowvoltage, PSD 914, the anode for SCR 900, is soft-shorted to P-Base 904,which is part of the cathode, causing a high amount of leakage.

One way to avoid the leakage shown in FIG. 9 is to place PSD 914 on theoutside of N-Sinker Region 918. In this configuration, however, the gainon the PNP portion of the SCR becomes very low, which does not allowproper SCR action.

Referring next to FIG. 1, a cross sectional diagram of a firstembodiment of a semiconductor controlled rectifier (SCR) 100 of thepresent invention is shown, having an increased immunity to the shortingeffects discussed above. Here and in the following discussion, SCRrefers to a semiconductor controlled rectifier rather than a siliconcontrolled rectifier, which is a special case of a semiconductorcontrolled rectifier. In general, reference to a semiconductor region as“heavily doped” means having a concentration of 10¹⁸/cm³ or greater.Likewise, “lightly doped” means a semiconductor region having aconcentration of less than 10¹⁸/cm³. In both cases, the doped regionsmay be formed by ion implantation or other methods as are well known tothose having ordinary skill in the art. Furthermore, the drawing figuresare not to scale but are drawn to clearly illustrate important featuresof the present invention. In the following discussion, the term“electrically connected” means an ohmic current path exists between twoor more cited elements and does not preclude the existence of resistors,parasitic elements, or other circuit elements within the current path asis well known in the art.

SCR 100 includes a p-type substrate (not specifically shown) and ann-type collector region that includes heavily doped n-type buried layer(NBL) 110, lightly-doped n-type epitaxial layer (NEPI) 108 and lightlydoped Region 106. N-type buried layer (NBL) 110 is again contacted byn-type Sinker 118, which receives highly-doped implants NSD, DEEPN andNBLX. Heavily doped p-type region P-Base 104 overlies N-type Region 106and heavily doped n-type region N-Emitter 102 overlies P-Base 104.

Heavily-doped p-type region PSD 114 is now isolated from n-type Region106 by a secondary heavily doped n-type Sinker 112, which is placedbetween PSD 114 and P-Base 104 and receives implants NSD and DEEPN (butnot the NBLX implant). Sinker 112 acts as a blocking junction for theleakage seen in the SCR of FIG. 9. Heavily doped p-type region PSD 114is thus blocked from leakage by Sinker 112. In order to enable SCRaction, two heavily-doped p-type regions, i.e., p-type deep well (DEEPP)116 and p-type buried layer extension (PBLX) 120 provide an anodejunction that extends partially under Sinker 112 to contact epitaxiallayer NEPI 108. The presence of modified Sinker 112 and anode junctionPBLX 120 relocates the current for SCR events deeper in the device. Itis, of course, possible to have leakage between P-Base 104 and PBLX 120in the current configuration, but this would occur at a higher voltagethan the rated voltage of the inherent transistor, so this is not agreat concern. Sinker Region 118 serves two purposes: it allows the SCRto be isolated from the substrate without needing deep trench isolation;and by having different resistance in series with Sinker 118 versusSinker 112, the trigger voltage of the SCR is decoupled from thepropensity of the SCR to inject current into the substrate.

In an example embodiment, typical doping used for each implant or layerin FIG. 1 can be as follows: N-Emitter is doped at between 5×10¹⁹/cm³and 10²⁰/cm³; P-Base at between 5×10¹⁷/cm³ and 10¹⁹/cm³; NEPI at between5×10¹⁵/cm³ and 10¹⁷/cm³; NBL at about 10¹⁹/cm³; NSD at about 10²⁰/cm³;DEEPN at between 5×10¹⁸/cm³ and 10¹⁹/cm³; NBLX at about 10¹⁸/cm³ orgreater; PSD at about 10²⁰/cm³; DEEPP at between 10¹⁸/cm³ and 10¹⁹/cm³;PBLX at between 10¹⁸/cm³ and 10¹⁹/cm³; and Region 106 at about 10¹⁵/cm³.Applicant notes, however, that the DEEPN implant used in Sinker 112 doesnot need to be as heavily doped as noted to serve as a blockingjunction; an implant in the range between 10¹⁶/cm³ and 10¹⁸/cm³ wouldalso work.

SCRs are typically connected as shown in FIG. 1, where a metallizationlayer forms Connector 122 that connects Sinker 118 (which forms the baseof an inherent PNP transistor) to PSD 114 (which forms the anode of theSCR). Sinker 118 and PSD 114 can be connected directly, as illustrated,or through a resistor (not specifically shown). The resistor or lackthereof determines how much the inherent PNP transistor turns on.Connection 124 to Sinker 112 is generally left floating to cause anycurrent to come from the p-type regions. When SCR 100 is turned on,i.e., during an ESD event, current flows from PSD Region 114 throughNEPI 108 and N-type Region 106 to P-Base 104 and then to N-Emitter 102.The disclosed SCR may provide one or more of the following benefits: theSCR is isolated; the design can allow independent control of triggercurrent and the amount of PNP injection from the substrate (as will bediscussed below); the production of the SCR does not require the use ofany additional masks; leakage issues are avoided; and the base bipolaron which he SCR is built is maintained, allowing for the same breakdownvoltage

FIG. 2 depicts a current-voltage diagram 200 of the SCR of FIG. 1, withthe horizontal axis showing the voltage and the vertical axisidentifying the current across the SCR. A 100 nanosecond TransmissionLine Pulse (TLP) is provided to SCR 100 and the I-V characteristics aremeasured. As shown, the voltage rises to approximately 6-7 volts withvery little current, then snaps back as the SCR is triggered. At thatpoint, the SCR goes into action and takes large amounts of current awayfrom the protected circuits.

The SCR of FIG. 1 can also be implemented with the dopant types beingreversed, i.e., with n-type dopants interchanged with p-type dopants andvice versa, as shown in FIG. 3. SCR 300 includes an n-type substrate(not specifically shown) and a p-type collector region that includesheavily doped buried layer PBL 310, lightly-doped epitaxial layer PEPI308 and lightly doped Region 306. Buried layer PBL 310 is contacted byp-type Sinker 318, which receives highly-doped implants PSD, DEEPP andPBLX. Heavily doped n-type region N-Base 304 overlies p-type Region 306and heavily doped p-type region P-Emitter 302 overlies N-Base 304.

Heavily-doped n-type region NSD 314 is now isolated from p-type Region306 by secondary heavily doped p-type Sinker 312, which is placedbetween NSD 314 and N-Base 304 and receives implants PSD and DEEPP (butnot the PBLX implant). Sinker 312 acts as a blocking junction for theleakage seen in the SCR of FIG. 9. Heavily doped N-type region NSD 314is thus blocked from leakage by Sinker 312. In order to enable SCRaction, heavily-doped n-type regions DEEPN 316 and NBLX 320 provide ananode junction that extends partially under Sinker 312 to contactepitaxial layer PEPI 308. The presence of modified Sinker 312 and anodejunction NBLX 320 relocates the current for SCR events deeper in thedevice. As noted earlier, it is possible to have leakage between N-Base304 and NBLX 320 in the current configuration, but this would occur at ahigher voltage than the rated voltage of the inherent transistor.

A variation on the connections in the disclosed embodiment is shown asSCR 400 in FIG. 4. In FIG. 1, Connector 124 was left floating; howeverin this embodiment, Connector 424 is switchably connected to Connector422, e.g., through a MOSFET (not specifically shown). It will beremembered that, as seen in FIG. 2, an embodiment of SCR 100 has atrigger voltage of about 6-7 volts. However, if this SCR is used in asystem having a normal operating voltage of, for example, 15 volt, theSCR will trigger at an undesirably low voltage. The disclosed switchbetween Connections 422 and 424 provides a way to modify the holding ortrigger current, allowing SCR 400 to be used in higher-voltagesituations. In normal operation, when the anode PSD 414 and extensionsDEEPP 116 and PBLX 120, inject carriers that reach P-Base 104, NEPI 108injects additional carriers. However, if the switch between Terminals422 and 424 is closed, some of the carriers are “stolen” by Sinker 112and do not contribute to the SCR action. Accordingly, when the switch isclosed, the trigger voltage shown in FIG. 2 can be stretched tosomething nearer to 30 volts, for example. The switch is designed to beclosed during normal operation of the circuit, but to open during ESDevents. It will be understood that although the doping of FIG. 4 isshown as corresponding to the doping of FIG. 1, the switchableconnection between Terminals 422 and 424 can also be used with thedoping profile of FIG. 3 or with any of the embodiments disclosedherein.

FIGS. 5-8 disclose plan views of the embodiment of FIG. 1, givingdifferent ways in which the layout of this device can be implemented. Itwill be understood that these plan views are equally applicable to theembodiment of FIG. 3 in which the polarity of the dopants is reversedand with or without the switchable connection to the secondary sinker.FIG. 5 discloses a basic implementation, while each of FIGS. 6-8 provideways in which punch-though can be improved near the edge of Deep TrenchIsolation.

As seen in SCR 500, N-Emitter 102 and P-Base 104 are shown extendinglaterally in this drawing, with P-Base 104 extending beyond N-Emitter102 in all four directions. Sinker 112, PSD 114 and Sinker 118 arelaterally isolated from P-Base 104 and from each other by Shallow TrenchIsolation 530, which laterally surrounds the entire SCR. PBLX 120, whichprovides the new anode junction, is shown as dotted lines. Additionally,Deep Trench Isolation 532, which is not shown in FIG. 1, isolates SCR500 from the rest of the chip.

FIG. 6 discloses SCR 600, in which Sinker 112 is extended at each end sothat Sinker 112 touches Deep Trench Isolation 532 to provide improvedpunch-through near the deep trench isolation. Other elements of the SCRare unchanged. FIG. 7 discloses SCR 700, in which the two segments ofSinker 112 are joined at each end to form Ring 734. Ring 734 laterallysurrounds P-Base 104. Another modification is shown in FIG. 8, whichdiscloses SCR 800 in which each of Sinker 112, PSD 114, and Sinker 118is laterally extended at their ends to form respective Rings 834, 836,and 838 respectively. In this configuration, the deep trench is notneeded to isolate the SCR from the substrate.

Other modifications to the circuit are also possible. Although a singleEmitter “finger” 102 is shown overlying P-Base 104, multiple Emitterfingers 102 can be placed within P-Base 104; the same can be true whenthe dopant type is reversed, as in FIG. 3. In one embodiment, the entireSCR structure can be repeated multiple times within the deep trenchisolation. Other variations will be obvious to one skilled in the art.

Although various embodiments have been shown and described in detail,the claims are not limited to any particular embodiment or example. Noneof the above Detailed Description should be read as implying that anyparticular component, element, step, act, or function is essential suchthat it must be included in the scope of the claims. Reference to anelement in the singular is not intended to mean “one and only one”unless explicitly so stated, but rather “one or more.” All structuraland functional equivalents to the elements of the above-describedembodiments that are known to those of ordinary skill in the art areexpressly incorporated herein by reference and are intended to beencompassed by the present claims. Accordingly, those skilled in the artwill recognize that the exemplary embodiments described herein can bepracticed with various modifications and alterations within the spiritand scope of the claims appended below.

What is claimed is:
 1. A bipolar semiconductor controlled rectifier(SCR) comprising: an emitter region having a first conductivity type andoverlying a base region having a second conductivity type different fromthe first conductivity type; a collector region having the firstconductivity type and lying under the base region, the collector regionincluding a buried layer of the first conductivity type and a firstconductivity type region; an anode region having the second conductivitytype; a first sinker region having the first conductivity type andcontacting the buried layer of the collector region, wherein the anoderegion is between the first sinker region and the base region; and asecond sinker region having the first conductivity type and contactingthe first conductivity type region of the collector region, the secondsinker region lying between the anode region and the base region,wherein an extension of the anode region extends under a portion of thesecond sinker region between the second sinker region and the buriedlayer.
 2. The bipolar SCR as recited in claim 1, further comprising afirst metallization that connects the anode region and the first sinkerregion.
 3. The bipolar SCR as recited in claim 2, further comprising asecond metallization that contacts the second sinker region.
 4. Thebipolar SCR as recited in claim 2, further comprising a secondmetallization contacting the second sinker region, wherein the secondmetallization is switchably connected to the first metallization.
 5. Thebipolar SCR as recited in claim 2, further comprising shallow trenchisolation that lies between the anode region and each of the firstsinker region and the second sinker region.
 6. The bipolar SCR asrecited in claim 2, further comprising deep trench isolation thatsurrounds the bipolar SCR.
 7. The bipolar SCR as recited in claim 6,wherein the shallow trench isolation separates the bipolar SCR from thedeep trench isolation.
 8. The bipolar SCR as recited in claim 7, whereinthe shallow trench isolation separates the first sinker, the anoderegion and the base region from the deep trench isolation and the secondsinker region contacts the deep trench isolation.
 9. The bipolar SCR asrecited in claim 6, wherein the shallow trench isolation separates thefirst sinker and the anode region from the deep trench isolation and thesecond sinker region extends laterally to encircle a region containingthe emitter region and the base region.
 10. The bipolar SCR as recitedin claim 5, wherein the second sinker region extends laterally toencircle a region containing the emitter region and the base region, theanode region extends laterally to encircle the second sinker region andthe first sinker region extends laterally to encircle the anode region.11. The bipolar SCR as recited in claim 5, wherein the bipolar SCR isrepeated multiple times within the deep trench isolation.
 12. Thebipolar SCR as recited in claim 1, wherein the first conductivity typeis n-type and the second conductivity type is p-type.
 13. The bipolarSCR as recited in claim 5, wherein the bipolar semiconductor controlledrectifier is a silicon controlled rectifier.
 14. A bipolar semiconductorcontrolled rectifier (SCR) comprising: an emitter region having a firstconductivity type and overlying a base region having a secondconductivity type different from the first conductivity type; acollector region having the first conductivity type and lying under thebase region; a first layer having the first conductivity type and lyingunder the collector region; a buried layer having the first conductivitytype and lying under the first layer; an anode region having the secondconductivity type and comprising a doped region of the secondconductivity type, a well region of the second conductivity type and afirst buried layer extension region of the second conductivity type, thefirst buried layer extension region contacting the first layer; a firstsinker having the first conductivity type and comprising a first sinkerregion, a first well region, and a second buried layer extension region,wherein the anode region is between the first sinker region and the baseregion; and a second sinker having the first conductivity type andcomprising a second sinker region, a second well region, and a thirdburied layer extension, wherein the first buried layer extension regionof the anode region extends under a portion of the second sinker. 15.The bipolar SCR as recited in claim 14, wherein the first and secondsinker regions have a dopant concentration of about 10²⁰/cm³.
 16. Thebipolar SCR as recited in claim 15 wherein the first well region has adopant concentration between 5×10¹⁸/cm³ and 10¹⁹/cm³ and the secondanode region has a dopant concentration between 10¹⁸/cm^(' and)10¹⁹/cm³.
 17. The bipolar SCR as recited in claim 16, wherein the firstburied layer extension region has a dopant concentration of 10¹⁸/cm³ orgreater and the second and third buried layer extension regions have adopant concentration between 10¹⁸/cm³ and 10¹⁹/cm³.
 18. The bipolar SCRas recited in claim 17 wherein the buried layer has a dopantconcentration of about 10¹⁹/cm³, the first layer has a dopantconcentration between 5×10¹⁵/cm³ and 10¹⁷/cm³, and the collector regionhas a dopant concentration of 10¹⁵/cm³.
 19. The bipolar SCR as recitedin claim 18 wherein the emitter has a dopant concentration between5×10¹⁹/cm³ and 10²⁰/cm³ and the base region has a dopant concentrationof between 5×10¹⁷/cm³ and 10¹⁹/cm³.
 20. The bipolar SCR as recited inclaim 19 wherein the first conductivity type is n-type and the secondconductivity type is p-type.